The present invention relates to methods and systems for conveying and selectively discharging food products. Further, the present invention relates to methods and systems for weighing and sorting food products.
Within industries such as foodstuffs industry, weighing and sorting machines have been described in publications such as U.S. Pat. No. 6,234,297, U.S. Pat. No. 6,015,049, WO 98/49892, U.S. Pat. No. 6,321,914, U.S. Pat. No. 5,526,437, U.S. Pat. No. 4,569,434, EP 0 593 126 and EP 0 900 601, all of which US patents are hereby incorporated in the present specification by reference.
In the foodstuffs industry there is a need for sorting products or articles at high speeds or throughputs according to various physical characteristics such as size, colour or weight, alternatively by any combination of these. Industrially packed food products, such as pieces of poultry, are often packed in packages of approximately equal weight, independent of the number of pieces included in the package. Therefore, many packages of food products include more than one individual product, i.e. the packages normally include at least two products. Some product packages, such as packages of chicken breast, typically include three pieces in each package, however, the number may be greater such as four or five pieces within the same package, as long as the packages all have approximately the same weight.
In order to ensure that food products of varying weight may be combined in packages having approximately the same weight, a multihead weigher may be used. In a multihead weigher, which in principal is known in the prior art, individual pieces of food products are randomly distributed among a large number, such as 5-50, preferably 8-20, of weighing systems. The weighing system typically has the form of receptacles. A computer is then used to calculate the most favorable combination of receptacles to reach a target weight, and the chosen receptacles are subsequently emptied such that the food products contained in the receptacle leave the receptacle and end up in a common package. It is thereby a need to keep the weight of the products contained within each receptacle as low as possible such that a large number of combinations are feasible. For an optimal number of combinations, it is a feature of the present invention that no more than one food product at a time is received within each receptacle.
In the applicant's international application WO 2006/092148 a weighing arrangement is shown having a dosing mechanism for controlled conveying of product material portions from an in feed to a weighing system. The dosing mechanism comprises a motor-driven transport screw formed as a helically shaped rod positioned in an open trough for conveying the product material.
Such dosing mechanisms as described above provide a very gentle and accurate delivery of products to the weighing system. However, in some situations the applicant has experienced that more than one product at a time may be delivered to the weighing system. The delivery of more than one product at a time to each receptacle may in particular occur when a plurality of products are located in an overlapping relationship. In case more than one product is located within a single receptacle, it will be more difficult to combine the content of the receptacle with the other pieces received within the other receptacles. In the worst case, no combination will be possible within the target weight and the content of the receptacle must be disposed of, which constitutes a loss of products, or re-circulated, i.e. re-directed to the in feed, which constitutes a loss of time and additional wear on the product. Further recirculation may eventually make the product unusable.